Nov. 21, 2017

Although the cost of wind energy has declined dramatically over the past two decades,
operation and maintenance costs are often higher than anticipated at an average of
half the power purchase agreement price. One of the primary drivers behind these costs
are wind turbine gearboxes, which often require repair or replacement well before
reaching their design life.

Guo and Keller assessed the behavior of the 750-kilowatt (kW) gearbox bearings through
modeling and testing in the 2.5-megawatt (MW) dynamometer. By introducing transient
braking and grid-loss conditions, the team found evidence of high stresses alternating
with low loads, torque reversals, and roller sliding—all of which can promote axial
cracks in the bearings.

"Focusing on these dynamic torque events during the design and operational phases
can be crucial to alleviate WEC formation and the resulting damage," says Guo.

The publication of Guo and Keller's journal article has generated industry interest
from SKF GmbH and the Winergy Drive Systems Corporation in participating in the next
phase of the research. For this campaign, an instrumented Winergy gearbox with SKF
bearings will be installed in the General Electric 1.5-MW SLE turbine at the National
Wind Technology Center this month. A wide range of operating conditions will be evaluated
during the 1-year validation campaign.

Results will be critical in further assessing the contribution of conditions such
as roller sliding, which will be directly measured inside the wind turbine, in addition
to loads in the development of WECs in wind turbine gearboxes.